Surface controlled subsurface safety valves commonly are installed in producing wells as a means of providing downhole protection against disasterous fires and blowouts due to failure, leakage or loss of surface equipment such as valves and flow lines. A safety valve of typical construction includes a body connected in the tubing and having a normally closed valve element that is held open in response to the pressure of fluid in a control line that extends outside the production tubing upwardly to a surface control unit. As long as the control line remains pressurized, the valve is open to the flow of production fluids. A reduction or loss of control line pressure due to the sensing of heat, collision or the like at the surface enables a coil spring to force a valve actuator in a direction to enable automatic closure of the valve element to shut in the well at the subsurface level of the safety valve.
Once closed, the valve element may be rather forcefully held against its seat because it is subjected to upward force due to the difference in pressures between production pressure and hydrostatic head of fluid in the tubing. To aid in reopening the valve element so that the well can be put back into production as soon as repairs have been made, an equalizing valve has been included that functions to equalize pressures above and below the valve element prior to opening the same by the application of control line pressure. In a known valve construction, the equalizing valve is in the form of a valve head on the actuator that engages a downwardly facing annular valve seat on the body to close off flow through an equalizing passage when the actuator is in the valve-closed position. Initial downward movement of the actuator in response to control line pressure moves the valve head off the seat to effect pressure equalization so that the valve element can be opened easily.
Although an equalizing valve is of considerable convenience to a well operator in putting the well back into production after the downhole safety valve has been closed, (either automatically as described above or deliberately for test purposes), it is subject to malfunction due to damage to the seal ring, cutting of the valve seat, and the like, as will be appreciated by those skilled in the art. When the equalizing valve becomes inoperable for any reason, the safety valve will not hold pressure due to leakage through the equalizing bypass passage. In order to repair the valve, it is necessary to pull the entire production string from the well, which is a time consuming, costly procedure that is highly undesirable.
It is the general object of the present invention to provide a new and improved subsurface valve system that includes an equalizing valve that can be retrieved to the surface for repair in the event of its malfunction without having to remove the safety valve or the production string from the well.